Iraqi forces push towards IS-held Mosul

Columns of Iraqi and Kurdish forces backed by US-led air strikes have slowly advanced on Mosul from several directions, launching a long-awaited operation to retake Iraq's second largest city from Islamic State (IS).

Iraq's elite counter-terrorism forces gather ahead of an operation to re-take the IS-held city of Mosul (AP)

Columns of Iraqi and Kurdish forces backed by US-led air strikes have slowly advanced on Mosul from several directions, launching a long-awaited operation to retake Iraq's second largest city from Islamic State (IS).

As air strikes sent plumes of smoke into the air and heavy artillery rounds rumbled, troops pushed into abandoned farming villages on the flat plains outside the city.

But they were slowed by roadside bombs and suicide car and truck bombs hurled at them by the militants.

The unprecedented operation is expected to take weeks, even months.

Though some of the forces are less than 30 kilometres (20 miles) from Mosul's edges, it was not clear how long it will take to reach the city itself.

Once there, they have to fight their way into an urban environment where more than one million people still live.

Aid groups have warned of a mass exodus of civilians that could overwhelm refugee camps.

Iraqi prime minister Haider Abadi announced the start of the operations on state television, launching the country's toughest battle since American troops withdrew from Iraq nearly five years ago.

"These forces that are liberating you today, they have one goal in Mosul, which is to get rid of Daesh and to secure your dignity," Mr Abadi said, addressing the city's residents and using the Arabic acronym for IS. "God willing, we shall win."

Mosul, Iraq's second largest city, fell to IS in the summer of 2014 as the militants swept over much of the country's north and central areas.

Weeks later the head of the extremist group, Abu Bakr al-Baghdadi, announced the formation of a self-styled caliphate in Iraq and Syria from the pulpit of a Mosul mosque.

If successful, the liberation of Mosul would be the biggest blow yet to IS.

Mr Abadi pledged the fight for the city would lead to the liberation of all Iraqi territory from the militants this year.

In Washington, US defence secretary Ash Carter called the launch of the Mosul operation "a decisive moment in the campaign" to defeat IS.

The US is providing air strikes, training and logistical support, but insists Iraqis are leading the charge.

More than 25,000 troops will be involved in the operation, launching assaults from five directions, according to Iraqi Brig Gen Haider Fadhil.

The troops include elite special forces who are expected to lead the charge into the city, as well as Kurdish forces, Sunni tribal fighters, federal police and state-sanctioned Shiite militias.

The Kurdish forces, known as peshmerga, advanced in long columns of armoured vehicles followed by hundreds of pick-up trucks on a cluster of some half a dozen villages east of the city on Monday.

Air strikes and heavy artillery pounded the squat, dusty buildings.

The area - historically home to religious minorities brutally oppressed by IS - was almost completely empty of civilians, allowing air power to do much of the heavy lifting.

But Lt Col Mohammad Darwish said the main roads and fields were littered with home-made bombs and that suicide car bomb attacks slowed progress.

Fighters entered the villages in Humvees but did not get out of their vehicles because it was too dangerous, a Peshmerga major said.

The IS-run new agency, Aamaq, said the group carried out eight suicide attacks against Kurdish forces and destroyed two Humvees belonging to the Kurdish forces and Shiite militias east of the city.

The Kurdish Rudaw TV broadcast images of Kurdish tanks firing on two trucks it said were IS suicide attackers. One of the trucks crashed into a tank and exploded. There was no immediate word on casualties from that attack or other fighting on Monday.

Just outside Baghdad - more than 225 miles (360 kilometres) south-east of Mosul - a suicide car bomber hit a checkpoint of security forces in the town of Youssifiyah, killing at least 12 people and wounding more than 30, officials said.

Iraqi army Lt Gen Talib Shaghati said the Mosul operation "is going very well", but declined to give details.

He said intelligence reports indicated that IS militants were fleeing towards Syria with their families.

IS once controlled nearly a third of Iraq and neighbouring Syria.

But over the past months their territory has been dramatically reduced.

In Iraq, their control is now limited to the area around Mosul and a few other small pockets.

For the Iraqi military, the battle is a test after two years of trying to rebuild from the humiliating defeat it suffered in the face of the IS blitz in 2014.

Mosul is also a test for the government's ability to control the multiple sectarian and ethnic tensions swirling around the conflict.

Mosul is a mostly Sunni city that was long a centre of bitterness against the Shiite-led government, fuelling insurgent and militant movements ever since the US-led invasion of Iraq in 2003.

While two years of IS rule may have left residents hating the militants, there is also little love for the government.

The role of the Shiite militias in the offensive has been particularly sensitive.

Shiite militia forces have been accused of carrying out abuses against civilians in other Sunni areas.

But Sunnis are also suspicious of the Kurds, who have ambitions to expand their self-rule area into Ninevah province, where Mosul is located.

Lt Col Amozhgar Taher, with the peshmerga, said his men would not enter Mosul itself because of "sectarian sensitivities".

Instead they will retake the villages to the east of the city, home to Christians and the Shabak, another minority group.

Iraqi special forces Lt Col Ali Hussein said the Kurdish forces are leading the first push on Mosul's eastern front. His men will probably wait another day or two near the town of Khazer.

US Lt Gen Stephen Townsend, commander of the anti-IS coalition, said in a statement it could take "weeks, possibly longer" to gain control of Mosul.

Military operations are predicted to displace 200,000 to a million people, according to the United Nations.

Near the eastern frontline, rows of empty camps line the road, ready to take in people fleeing.

But aid groups say they only have enough space for some 100,000 people.

In Geneva, a senior UN humanitarian official, undersecretary-general Stephen O'Brian, said he is "extremely concerned" for the safety of civilians in Mosul.

He said families are at "extreme risk" of being caught in crossfire, tens of thousands may end up besieged or held as human shields, and thousands could be forcibly expelled.

In the midst of financial crisis, the Iraqi government says it lacks the funds to adequately prepare for the humanitarian fallout.

In some cases commanders say they are encouraging civilians to stay in their homes rather than flee.

"While we may be celebrating a military victory" after Mosul is liberated, "we don't want to have also created a humanitarian catastrophe," said Falah Mustafa, the foreign minister for Iraq's Kurdish region.